Laser-Produced Porous Surface

ABSTRACT

An implant having a porous tissue ingrowth structure and a bearing support structure is disclosed. The implant includes a metal insert having a bone ingrowth structure, an intermediate structure and a bearing support structure. A bearing surface is formed from a polymer material and attached to the bearing support structure. The intermediate structure has a porosity sufficient to inhibit the polymer material from translating through the bearing support structure to the bone ingrowth structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.11/295,008, filed on Dec. 6, 2005, the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a device having a porous surfaceattached directly or indirectly to a bearing surface and a method forforming the same.

In particular, this invention relates to a computer-aided laserapparatus or other suited high energy beam, which sequentially remelts aplurality of powder layers to build a porous layer in a layer-by-layerfashion.

The present invention also includes a method of attaching or connectinga bearing surface directly or indirectly preferably formed from apolymer to the sequentially-built porous part.

The present application is particularly directed toward a method offorming a porous and partially-porous metallic structure having abearing surface.

The field of free-form fabrication has seen many important recentadvances in the fabrication of articles directly fromcomputer-controlled databases. These advances, many of which are in thefield of rapid prototyping of articles such as prototype parts and molddies, have greatly reduced the time and expense required to fabricatearticles, particularly in contrast to conventional machining processesin which a block of material, such as a metal, is machined according tothe engineering drawings. One example of a modern rapid prototypingtechnology is the selective laser sintering process practiced by systemsavailable from 3D Systems, Valencia, Calif. According to thistechnology, articles are produced in a layer-wise fashion, from alaser-fusible powder that is dispensed one layer at a time. The powderis fused, remelted or sintered, by the application of laser energy thatis directed in raster-scan fashion to portions of the powder layercorresponding to a cross-section of the article. After fusing of thepowder on one particular layer, an additional layer of powder isdispensed, and the process repeated with fusion taking place between thecurrent layer and the previously laid layers, until the article iscomplete.

The field of rapid prototyping of parts has, in recent years, made largeimprovements in broadening high strain, high density parts for use inthe design and pilot production of many useful articles including metalparts. These advances have permitted the selective laser remelting andsintering process to now also be used in fabricating prototype toolingfor injection molding, with expected tool life in excess of 10,000 moldcycles. The technologies have also been applied to the directfabrication of articles, such as molds from metal powders without abinder. Examples of metal powder reportedly used in such directfabrication include two-phase metal powders of the copper-tins,copper-solder (the solder being 70% lead and 30% tin), and bronze-nickelsystems. The metal articles formed in these ways have been quite dense,for example, having densities of up to 70% to 80% of full density (priorto any infiltration). Prior applications of this technology have strivedto increase the density of the metal structure formed by the melting orsintering process. The field of rapid prototyping of parts has focusedon providing high strength, high density parts for use and design inproduction of many useful articles, including metal parts.

But while the field of rapid prototyping has focused on increasingdensity of such three-dimensional structures, the field has not focusedits attention on reducing the density of three-dimensional structures.Consequently, applications where porous and partially-porous metallicstructures, and more particularly metal porous structures withinterconnective porosity, are advantageous for use, have been largelyignored.

In addition, many structures, especially in the medical arts, requiretwo different surfaces, each adapted for their own purposes. Along thisline, a structure may have a first surface which needs to be porous fortissue in-growth and a second surface which should be adapted to be abearing surface. Further, the first surface or portion may includedifferent layers having different gradients of porosity. For example,the first surface may include an outer region having a porosity ofapproximately 80%. As you move normal with regard to the first surfacethe porosity may alter such that the porosity is increased or in apreferred embodiment, the porosity decreases even until the porosity isalmost zero. Of course, the present invention contemplates a situationwhere the porosity alters from position to position depending on therequirements of the device.

Although different techniques have tried to provide such a method andapparatus, still greater techniques are needed in this area.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, the present invention relates to a method of formingan implant having a porous tissue ingrowth structure and a bearingsupport structure. The method may include depositing a first layer of ametal powder onto a substrate. Next, a laser beam scans over the powderso as to sinter the metal powder at predetermined locations. At leastone layer of the metal powder may be deposited onto said first layerwhile repeating the laser scanning step for each successive layer untila predetermined structure having a first surface and a second surface isconstructed. A flowable polymer is placed into contact with the secondsurface of said predetermined structure. The polymer is cooled such thatthe flowable polymer adheres to the second surface of the structure. Thelaser scanning step may include scanning the laser beam onto the metalpowder to form a portion of a plurality of predetermined unit cellswithin the metal powder.

The method may include placing the predetermined structure into a cavityof a die and depositing a polymer onto the second surface of thepredetermined structure within the cavity of the die. The step ofplacing a flowable polymer in contact with the second surface of thepredetermined structure may include applying pressure and heat to thepolymer in the cavity of the die. The step of placing the flowablepolymer in contact with the second surface of the predeterminedstructure may include transferring the flowable polymer onto the secondsurface. The step of placing the flowable polymer in contact with thesecond surface of the predetermined structure may include placing thesecond surface of the predetermined structure adjacent a polymerstructure, applying heat to the polymer structure and allowing thepolymer structure to engage the predetermined structure. Thepredetermined structure may include an outer layer, an intermediatelayer and an inner layer, the outer layer and the inner layer beingrelatively porous and the intermediate layer being relatively dense suchthat the flowable polymer cannot substantially leech through theintermediate layer from the inner layer to the outer layer. The outerlayer has a porosity approximately between 60% to 80% and the innerlayer has a porosity approximately higher than 80%. The outer layer mayhave a pore size distribution in the range of 80 μm to 800 μm and theinner layer may have a pore size distribution higher than approximately800 μm.

The predetermined structure may have a gradient porosity. The gradientporosity of the predetermined structure may include a first layer thatis substantially porous, a second layer that is substantiallynon-porous, a third layer that is substantially porous such that theflowable polymer cannot substantially leech through the second layerfrom the third layer to the first layer when the flowable liquid polymeris placed in contact with the third layer.

The present invention also includes a medical implant including a metalinsert having a bone ingrowth structure, an intermediate structure and abearing support structure, the bone ingrowth structure having a porositysufficient to promote bone ingrowth. The implant also includes a bearingsurface formed from a polymer material, the bearing surface beingattached to the bearing support structure. The intermediate structurehas a porosity sufficient to inhibit the polymer material fromtranslating through the bearing support structure to the bone ingrowthstructure. The intermediate structure may be designed to facilitate aspecific stiffness characteristic to an overall construct and/or includetwo barrier layers and a bridging section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is one embodiment of a metal insert of an acetabular cupconstructed according to the present invention;

FIG. 1B illustrates a cut out portion of the metal insert of FIG. 1A;

FIG. 1C is a unit cell used to construct a portion of the metal insertof FIG. 1A;

FIG. 1D is a computer model of a portion of an acetabular cupconstructed using the unit cell of FIG. 1C;

FIG. 1E is a unit cell used to construct a portion of the metal insertof FIG. 1A;

FIG. 1F is a computer model of a portion of an acetabular cupconstructed using the unit cell of FIG. 1E;

FIG. 1G is a computer rendering of an acetabular cup including theportions illustrated in FIGS. 1D and 1F;

FIG. 2 is a schematic drawing of a pelvis region;

FIG. 3 is a schematic drawing of an acetabular cup and a femoral stemimplanted into the pelvic region;

FIG. 4 is an illustration of an apparatus used in conjunction with thepresent invention;

FIG. 5 illustrates an alternate apparatus for employing methods of thepresent invention;

FIG. 6 is a sample of constructed coupons using a method according tothe present invention;

FIG. 7 is a table showing a series of parameters used for making samplesaccording to the present invention;

FIGS. 8A-8C are scanning electro-microscopic images of the surfacestructure of various samples made by a method according to the presentinvention;

FIG. 9A-9D are illustrations of different embodiments of unit cellsaccording to the present invention;

FIG. 10 illustrates a lattice structure using a plurality of unit cellsaccording to FIG. 8A;

FIG. 11 illustrates a lattice structure with and without laser beamcompensation using the unit cells illustrated in FIG. 1;

FIG. 12 illustrates a lattice structure using a plurality of unit cellsillustrated in FIG. 8B;

FIG. 13 illustrates a lattice structure with and without laser beamcompensation using the unit cell of FIG. 8B;

FIG. 14 illustrates a lattice structure using a plurality of unit cellsillustrated in FIG. 8C;

FIGS. 15A and 15B illustrate lattice structures created using unit cellsillustrated in FIGS. 9D and 8A with varying exposure time, respectively;

FIG. 15C illustrates a side view of the embodiment of FIG. 15A;

FIG. 15D illustrates a side view of the lattice structure illustrated inFIG. 15B;

FIG. 16 is a representation of a lattice structure created using aplurality of unit cells illustrated in FIG. 8D with random perturbation;

FIG. 17 is an illustration of an acetabular cup built using the methodsof the present invention;

FIG. 18 is an illustration of an alternate embodiment of an acetabularcup built using the methods of the present invention;

FIG. 19 is an illustration of an alternate embodiment of an acetabularcup built using the methods of the present invention;

FIGS. 20 and 21 are representations of a patella component built usingone embodiment of the present invention.

FIG. 22 is a side view of a cartilage plug built according to oneembodiment of the present invention;

FIG. 23 is a front view of the cartilage plug of FIG. 22; and

FIG. 24 is an illustration of an alternate embodiment of an acetabularcup.

DETAILED DESCRIPTION

The present invention relates to a method of forming a porous orpartially porous metallic structure having a bearing surface attacheddirectly or indirectly thereto. The structures are particularly but notexclusively applicable for use in the art of soft tissue interlockstructures for medical implants and prosthesis.

The method makes use of laser technology or any other high energy beamby employing a variety of scanning strategies.

Typical metal and metal alloys employed include stainless steel, cobaltchromium alloys, titanium and its alloys, tantalum and niobium, all ofwhich have been used in medical device applications. The presentinvention can be used for such medical device applications where boneand/or soft tissue interlock with the component is required, or where acontrolled structure is required to more closely match mechanicalproperties of the device with surrounding tissue.

Additionally, the present invention may be employed to enhance thebiocompatibility of a porous structure with human tissue while alsoproviding a bearing surface that is resistant to wear. With theseadvantages in mind, a structure may be created using specific dimensionsrequired to accommodate a particular patient.

The porous and partially porous metallic structures may be attached orincorporated to a surface, which will be used as a bearing surface, asis described below. By interconnecting or having an implant with aporous structure adjacent a bearing surface, the orthopedic implant canprovide a structure for permitting bone and soft tissue interlock incombination with a bearing surface that enables the implant to rotate,articulate or pivot relative to an additional bearing surface.

As shown in FIGS. 1A and 1B, the device for implantation into the bodymay be in the form of an acetabular cup 10. The acetabular cup 10preferably includes a metal insert 11 comprised of a bearing supportstructure 12, a bone ingrowth structure 14 and an intermediate structure16. The acetabular cup 10 can be used in a total hip replacementsurgery.

During the surgery, the joint of the hip, as shown in FIGS. 2 and 3, thehip socket 20 (acetabulum) and the ball 18 or head of the femur F areremoved. An acetabular cup, such as acetabular cup 10, is positionedwithin the pelvis P. A first end 15 of a femoral stem FS is positionedwithin the femur F, while a second end 17, including a “ball” ispositioned adjacent the bearing support structure 12 of the acetabularcup 10. Desirably, the second end 17 of the femoral stem FS is rotatablymoveable relative to the acetabular cup 10.

The bone ingrowth structure 14, as well as the bearing support structure12 and intermediate structure 16 of the acetabular cup 10 may beconstructed using a direct laser remelt process as, for example,described in U.S. patent application Ser. No. 10/704,270, filed Nov. 7,2003 entitled “Laser-Produced Porous Surface,” and U.S. patentapplication Ser. No. 11/027,421, filed Dec. 30, 2004, entitled“Laser-Produced Porous Structure,” the disclosures of which are herebyincorporated herein by reference.

As shown in FIG. 1A, in one preferred embodiment of the presentinvention, the bone ingrowth structure 14 is approximately 1.1 mm thickand has a porosity of approximately between the range of 70% to 80%. Theintermediate structure 16 is approximately 0.1 mm thick and issubstantially fully dense. The bearing support structure 12 isapproximately 0.8 mm thick and is adapted for being secured within apolymer layer to form a bearing surface 8, as will be described below.The incorporation of the polymer, as described below, desirably resultsin an acetabular cup with a thickness of less than 4 mm, which isconsidered to be preferentially for resurfacing cups. The measurementsare simply illustration and should not be considered a limitation sincevarious thicknesses may be used when building the part.

The bone ingrowth structure 14 may be prepared by populating the volumeof the structure with a single unit repeating cell using proprietysoftware. A single unit cell 110 and the corresponding porous layer areshown in FIGS. 1C and 1D. The single cell 110 used is a unit celloctahedron structure having a length of 800 μm with vertical pillars oneach corner. When tessellated, these cells produce porous structureshaving a porosity of approximately 80% with full interconnected porosityand mean pore sizes between 100 μm and 400 μm.

The intermediate structure 16 is designed to facilitate the bonding ofthe bearing support structure 12 to the bone ingrowth structure 12, aswell as isolate the bone ingrowth structure from a polymeric material,as will be described below.

The bearing support structure 12 may be designed by populating thevolume of the structure with a single repeating unit cell 112, as shownin FIGS. 1E and 1F. This produces a structure that is between 90% to 95%porous with fully interconnected porosity with pore sizes between 1.25mm and 2 mm diameter. Of course, the dimension of the unit cell 112 maybe altered or even a difference unit cell employed, such that theporosity of the structure may be customized based on desirability.

The porosity of each structure may be altered but in a preferredembodiment the porosity of each structure is dependent on thatstructures function. Thus the resultant porosity of the bone ingrowthstructure 14 should be within a range that promotes bone ingrowth. Theporosity of the bearing support structure 12 should be in a range thateasily allows for a polymeric material or other material to adhere tothe structure as will be described below. And the porosity of theintermediate layer should be in a range that prohibits or at leastreduces the ability of a polymeric material to leech from the bearingsupport structure 12 to the bone ingrowth structure 14, as will bedescribed below.

The files describing the bone ingrowth structure 14, solid intermediatestructure 16 and the bearing support structure 12 may all be loaded intothe operating software for a MCP realizer, FUSCO. The three structuresare then reassembled and manufactured as one part. A schematic of themanufactured part and a photo of the final component are shown in FIG.1G.

In one specific embodiment, the acetabular cup has a total thickness of3 mm and an internal diameter of 46 mm.

According to one method of forming a porous three-dimensional structureby laser melting, a powder of titanium, titanium alloys, stainlesssteel, cobalt chrome alloys, tantalum or niobium is disposed onto asubstrate. The laser melting process includes scanning a laser beam ontothe powder and in parallel scan lines with a beam overlap, e.g., scanspacing, followed by similar additional scans or subsequent scans at 90degrees, as way of example. The type of scan chosen may depend on theinitial layer thickness as well as the web height required. The webheight refers to the height of a single stage of the metal structure 11.The web height may be increased by depositing additional layers ofpowder of a structure and scanning the laser at the same angle of theprevious scan. Further, the additional scan lines may be at any angle tothe first scan, to form a structure with the formation of a definedporosity, which may be regular or random. The scanned device may beprogrammed to proceed in a random generated manner to produce anirregular porous construct but with a defined level of porosity.Furthermore, the scan can be preprogrammed using digitized images ofvarious structures, such as the acetabular cup 10, shown in FIGS. 1A and1B, to produce a similar structure. The scan may also be customized to aparticular patient. In this process, a CT scan of for instance, aperson's acetabullum is taken and inputted into a computer program. Theresultant file may be sliced, digitized or manipulated by methods knownto those in the art as well as described herein. Based on these filesand tailored measurements, a customized implant may be fabricated for aparticular individual.

To produce a bone ingrowth structure, such as the bone ingrowthstructure 14 of the acetabular cup 10, the nature of the material formedas a result of laser melting of powder beads is principally dependentupon the thermal profile involved (heating rate, soaking time, coolingrate); the condition of the raw material (size and size distribution ofpowder particles); atmospheric conditions (reducing, inert or oxidizingchamber gas); and accurate control of the deposited layer thickness.

The most optimum porous structure for maximization of bone in-growth ona prosthesis has generally been found to be between approximately 60% to80%. The preferred pore structure is irregular and interconnected, witha minimum pore size between about 80 μm and 100 μm and a maximum poresize between 80 μm and 800 μm.

The bone ingrowth structure 14, the bearing support structure 12 and theintermediate structure 16 of the acetabular cup 10 may be constructedusing the apparatus shown in FIGS. 4 of 5. The apparatus of FIG. 4 mayinclude an Nd; YAG industrial laser 30, integrated to an RSG 1014 analoggalvo-scanning head 32 for providing a maximum scan speed of 500 mm persecond. The laser beam 34 is directed into an atmospherically-controlledchamber 36, which consists of two computer-controlled platforms withpowder delivery and part building. The powder is delivered from avariable capacity chamber 38 into the chamber 36 and is transported by aroller 40 to a build platform 42 above a variable capacity build chamber44.

In one embodiment as shown in FIG. 4, the build and delivery systemparameters are optimized for an even 100 μm coating of powder to bedeposited for every build layer. For implant manufacture, the metalschosen as surface materials are all difficult to process due to theiraffinity for oxygen. Titanium and other alloys are easily oxidized whenprocessed by laser in oxygen-containing atmosphere, their oxide productshave high melting points and poor flowability. For this reason, and toprevent the formation of other undesirable phases, the methods may becarried out under an Argon inert atmosphere in chamber 36. Pressure mayremain at or below atmospheric pressure during the entire application.In another example of forming a porous structure, a cobalt chrome alloymay be configured into square structures, called coupons. As shown inFIG. 6, an array of cobalt chrome coupons may be built onto a stainlesssteel substrate. The coupons were built as test subjects. The cobaltchrome alloy may have a particle size distribution of 90 less than 22μm, i.e., 90% of the particles are less than 22 μm, the composition ofwhich is shown in the table below.

TABLE 1 Composition of Co212-e CoCr alloy Element Cr Mo Si Fe Mn Ni N CCo Wt % 27.1 5.9 0.84 0.55 0.21 0.20 0.16 0.050 Balance

An array of nine sample coupons were produced as shown in FIG. 6, withthe process of Table 2, using a maximum laser power of 78 watts (W) andlaser scanning speed for each coupon varying between 100-260 mms⁻¹. Ofcourse a higher laser power may be employed; however, a higher laserpower would also necessitate increasing the speed of the laser scanspeed in order to produce the desired melting of the powder layer. Asimple linear x-direction scan was used on each of the coupons. Thisallowed the processing parameter, beam overlap, to be used to controlthe space between successive scan lines. That is, with a 100 μm laserspot size, an overlap of −200% produces a 100 μm gap between scans.Although the acceptable range for the beam overlap is given at +50% to−1200% it should be duly noted that the negative number only refers tothe fact the there is a gap as opposed to a beam overlap betweensuccessive scans. For instance a beam overlap of zero refers to the factthat successive scans on the same layer of powder border each other. Apositive beam overlap produces more solid components in contrast to amore negative beam overlap, which produces a more porous structure. Theless the beam overlap the more solid the resultant structure will be. Inaddition, a larger beam overlap may be used to create the attachmentstructure or bearing support structure 12, as compared to theintermediate structure 16. If the beam overlap was 5%, then 5% of thefirst scan is overlapped by the second scan. When computing the Andrewnumber the absolute value of the beam overlap is used. The complete setof process parameters used is shown in Table 2 below.

TABLE 2 Process parameters Overlap Power Layer Beam Scanning (% of WattsThickness Diameter Speed Atmos- No. of line (W) (μm) (μm) (mms⁻¹) phereLayers width) 78 100 100 100-260 No 16 25, 50, −500

The incremental changes in scanning speed and the size of the speedrange were modified as the experiments progressed. To begin with, alarge range of speeds was used to provide an initial indication of thematerial's performance and the propensity to melt. As the experimentsprogressed, the range was reduced to more closely define the processwindow. Speed and beam overlap variations were used to modify thespecific energy density being applied to the powder bed and change thecharacteristics of the final structure. The complete series ofparameters are given in FIG. 7, the parameters sets used for thedefinitive samples are shaded in gray.

The key laser parameters varied for forming the three-dimensionalmetallic porous structures are: (a) Laser scanning speed (v.) in(mms⁻¹), which controls the rate at which the laser traverses the powderbed; (b) Laser power, P(W), which in conjunction with the laser spotsize controls the intensity of the laser beam. The spot size was keptconstant throughout the experiment; (c) Frequency, (Hz) or pulserepetition rate. This variable controls the number of laser pulses persecond. A lower frequency delivers a higher peak power and vice versa.

The line width can be related to the laser scanning speed and the laserpower to provide a measure of specific density, known as the “AndrewNumber”, where:

${An} = {\frac{P}{b \times v}\left( {J/{mm}^{- 2}} \right)}$

Where P denotes the power of the laser, v is the laser scanning speedand b denotes beam width of the laser. The Andrew number is the basisfor the calculation of the present invention. The Andrew number may alsobe calculated by substituting the line separation (d) for beam width(b). The two methods of calculating the Andrew number will result indifferent values being obtained. When using line separation (d) as afactor only one track of fused powder is considered, whereas when usingthe beam width (b) as a factor, two tracks of fused powder areconsidered as well as the relative influence of one track to the next.For this reason we have chosen to concern ourselves with the Andrewnumber using scan spacing as a calculating factor. It can thus beappreciated, that the closer these tracks are together the greater theinfluence they have on one another.

Additionally, the laser power may be varied between 5 W and 1000 W.Utilizing lower power may be necessary for small and intricate parts butwould be economically inefficient for such coatings and structuresdescribed herein. It should be noted that the upper limit of laser poweris restricted because of the availability of current laser technology.However, if a laser was produced having a power in excess of 1000 W, thescanning speed of the laser could be increased in order that anacceptable Andrew number is achieved. A spot size having a range between5 μm to 500 μm is also possible. For the spot size to increase whilestill maintaining an acceptable Andrew number, either the laser powermust be increased or the scanning speed decreased.

The above formula gives an indication of how the physical parameters canvary the quantity of energy absorbed by the powder bed. That is, if themelted powder has limited cohesion, e.g. insufficient melting, theparameters can be varied to concentrate the energy supply to the powder.High Andrew numbers result in reduced pore coverage and an increase inpore size due to the effects of increased melt volume and flow. LowAndrew numbers result in low melt volume, high pore density and smallpores. Current satisfactory Andrew numbers are approximately 0.3 J/mm⁻²to 8 J/mm⁻² and are applicable to many alternative laser sources. It ispossible to use a higher powered laser with increased scanning speed andobtain an Andrew number within the working range stated above.

Line spacing or beam overlap can also be varied to allow for a gapbetween successive scan lines. It is, therefore, possible to heatselected areas. This gap would allow for a smaller or larger pore sizeto result. The best illustration of this is shown in FIGS. 8A to 8Cwhere a −500% beam overlap has been applied. FIGS. 8A to 8C are scanningelection microscope images of the surface structure of CoCr on stainlesssteel produced with a laser power of 82 W cw.

FIG. 8A was produced with a laser scanning speed of 105 mms⁻¹ and FIG.8B was produced with a laser scanning speed of 135 mms⁻¹. FIG. 8C is animage of the same structure in FIG. 8B, in section. There is asignificant self-ordering within the overall structure. Larger columnarstructures are selectively built leaving large regions of unmeltedpowder. It is worth noting that these pillars are around 300 μm wide,over 1.6 mm tall and fuse well with the substrate, as seen in FIG. 8C.Further analysis shows that the use of a hatched scanning format allowsporosity to be more sufficiently controlled to allow the pore size to bedirectly controlled by the beam overlap.

The use of an optical inspection method to determine this approximateporosity is appropriate given the sample size. This method, although notaccurate due to the filter selection process, can, if used carefully,provide an indication of porosity. This porosity level falls within therange of the desired porosity for bone ingrowth structures. Themechanical characteristics of the porous structures are determined bythe extent of porosity and the interconnecting webs. A balance of thesevariables is necessary to achieve the mechanical properties required bythe intended application.

Increased fusion may, if required, be obtained by heating the substrate,powder or both prior to scanning. Such heating sources are commonlyincluded in standard selective laser sintering/melting/remeltingmachines to permit this operation.

As described above, the process can be carried out on flat baseplatesthat provide for easy powder delivery in successive layers of around 100μm thickness. Control of powder layer thickness is very important ifconsistent surface properties are required. The application of thistechnology can also be applied to curved surfaces such as those found inmodern prosthetic devices such as acetabular cup 10, with refinementsbeing made to the powder layer technique.

The structures may receive ultrasonic and aqueous cleaning. On closeexamination, the resultant porous surfaces produced by the Direct LaserRemelting process exhibit small particulates that are scatteredthroughout the structure. It is unclear at this stage whether theseparticulates are bonded to the surface or loosely attached but there aremeans to remove or consolidate the particulates if required, by forexample acid etching, heat treatment, a combination of the two, or thelike.

The Direct Laser Remelting process has the ability to produce porousstructures that are suitable for bone in-growth applications. Thepowdered surfaces have undergone considerable thermal cyclingculminating in rapid cooling rates that have produced very finedendritic structures.

The Direct Laser Remelting process can produce effective bone in-growthsurfaces and the manufacturing costs are reasonable.

In the preceding examples, the object has been to provide a metal inserthaving a porosity on a base but the present invention can also be usedto provide a non-porous structure on such a base to form athree-dimensional structure. The same techniques can be utilized for thematerials concerned but the laser processing parameters can beappropriately selected so that a substantially solid non-porousstructure is achieved.

Again, a technique can be used to deposit the powder onto a suitablecarrier, for example a mold, and to carry out the process without theuse of a base so that a three-dimensional structure is achieved whichcan be either porous, as described above, or non-porous if required.

It will be appreciated that this method can, therefore, be used toproduce article from the metals referred to which can be created to adesired shape and which may or may not require subsequent machining. Yetagain, such an article can be produced so that it has a graded porosityof, e.g., non-porous through various degrees of porosity to the outersurface layer. Such articles could be surgical prostheses, parts or anyother article to which this method of production would be advantageous.

Although the porous structure has been discussed with regard to randomlydepositing powder onto a substrate and selectively laser melting thepowder while repeating layer after layer, in contrast, each layer orportion of a layer, may be scanned to create a portion of a plurality ofpredetermined unit cells. As successive layers of powder are depositedonto previous layers, the scanning and depositing of such layerscontinues the building process of a predetermined unit cell. Whenconstructing the predetermined unit cells, the preferred embodimentincludes employing a pulse high energy beam to form “spots” on thedeposited powder layer. At least some of the “spots” are joined toproduce struts or portions of struts, which constitute a portion of apredetermined unit cell. The spots may be created at random, in acontinuous manner or a combination of the two. Examples of some possiblegeometric shapes of a unit cell are shown in FIGS. 9A-9D. As disclosedherein, by continuing the building process refers not only to acontinuation of a unit cell from a previous layer but also a beginningof a new unit cell as well as the completion of a unit cell.

The invention can include a laser melting process that precludes therequirement for subsequent heat treatment of the structure, therebypreserving the initial mechanical properties of the core or base metal.The equipment used for the manufacture of such a device could be one ofmany currently available including the MCP Realiszer, the EOS M270,Trumpf Trumaform 250, the Arcam EBM S12 and the like. The laser may alsobe a custom produced laboratory device.

As shown in FIG. 5, one apparatus for constructing a structure comprisedof predetermined unit cells may include a chamber 50 filled with aninactive gas such as argon and nitrogen. By using an inactive gas youcan avoid oxidation of the metal powder 52. The three-dimensional model,such as metal insert 11 may be built on a base plate 51. The model isbuilt in a layer by layer fashion.

As successive layers of metal powder are deposited onto previous layers,the laser head 53 projects a beam of energy 54 onto locations of thepowder to thereby form a spot or portion of a strut of a predeterminedunit cell. The laser scans the powder bed and projects the energy beambased on the slice data of the model contained in the computer program.

After a layer has been completed, successive layer of metal powder maybe deposited onto the previous layer by the use of a powder feeder 55.The powder feeder 55 may work in conjunction with a piston 56 that islowered prior to the depositing of the additional layer of metal powder.The piston 56 is desirably positioned under the substrate on which themetal structure is built. As each layer is processed, the piston 56 maybe lowered and an additional layer of metal powder deposited onto theprevious layer. In this manner, each layer of unprocessed powder ispositioned at the same distance from the laser head 53. The laser beamis capable of being directed along a X, Y coordinate system such thatthe desired location of the layer of metal powder can be engaged by thebeam of energy 54. The guiding of the laser beam is dependent on themanufacturing system used. For example, if an E-beam system is employedthe movement of the E-beam is controlled by deployment of the magneticfields. If a laser beam apparatus is employed, the movement or guidanceof the laser beam is controlled by a galvanometer.

The pore density, pore size and pore size distribution can be controlledfrom one location on the structure to another. It is important to notethat successive powder layers can differ in porosity by varying factorsused for laser scanning powder layers. Additionally, the porosity ofsuccessive layers of powder can be varied by either creating a specifictype of predetermined unit cell or manipulating various dimensions of agiven predetermined unit cell.

As described in U.S. patent application Ser. No. 11/027,421, thedisclosure of which is incorporated by reference herein, such unit cellsdesigns can be a tetrahedron 60 (FIG. 9A), dodecahedron 62 (FIG. 9B),octahedron 64 (FIG. 9C), diamond, as well as many other various shapes.In addition, various struts may be removed from a unit cell to create anadditional structure such as that shown in FIG. 9D. Besides regulargeometric shapes as discussed above, the unit cells of the presentinvention may be configured to have irregular shapes where various sidesand dimensions have little if any repeating sequences. The unit cellscan be configured to build constructs that closely mimic the structureof trabecular bone for instance. Unit cells can be space filling, allthe space within a three-dimensional object is filled with cells, orinterconnected where there may be some space left between cells but thecells are connected together by their edges. The unit cells can also beconstructed in a form of a lattice. Additionally, adjacent lattices maybe isolated from one another or only partially attached.

The cells can be distributed within the construct a number of ways.Firstly, they may be made into a block within a computer added design(“CAD”) system where the dimensions correspond to the extent of thesolid geometry. This block can then be intersected with the geometryrepresenting the component to produce a porous cellular representationof the geometry. Secondly, the cells may be deformed so as to drape overan object thus allowing the cells to follow the surface of the geometry.Thirdly, the cells can be populated through the geometry following thecontours of any selected surface.

The unit cell can be open or complete at the surface of the construct toproduce a desired effect. For instance, open cells with truncatedlattice struts produce a surface with a porosity and impart the surfacewith some degree of barb, whereas closed cells can be “peaky” so as toincrease surface roughness.

Modifying the lattice strut dimensions can control the mechanicalstrength of the unit cell. This modification can be in a number of keyareas. The lattice strut can be adjusted by careful selection of buildparameters or specifically by changing the design of the cross-sectionof each strut. The density of the lattice can similarly be adjusted bymodification of the density of the unit cells as can the extent andshape of porosity or a combination thereof. Clearly the overall designof the unit cell will also have a significant effect of the structuralperformance of the lattice. For instance, dodecahedral unit cells have adifferent mechanical performance when compared to a tetrahedral(diamond) structure.

As shown in FIG. 9A, in a tetrahedron 60, each point 70, 72, 74, and 76is the same distance from the neighboring point. This structure isanalogous to the arrangements of carbon atoms in diamond.

Each carbon atom in the diamond structure is surrounded by four nearestneighbors. They are connected together by bonds that separate them by adistance of 1.5445 angstroms. The angles between these bonds are 109.5degrees. As a result, the central atom and its neighbors form atetrahedron. This geometry as in the case discussed herein may then bescaled to appropriate value for the pore construct required.

The two key parameters used to define the relations regarding height,surface area, space height, volume of tetrahedron, and the dihedralangle of a tetrahedron are the strand length of the tetrahedron and,i.e., the diameter or height and width, cross section area of the strandi.e., strut. These two parameters control the pore size and porosity ofthe structure. The parameter editor and relation editor within a typicalCAD system can be used to control these parameters. Hence, by changingthe parameters one can change the fundamental properties of the porousstructure. As shown in FIG. 9A, the diamond structure may have acircular cross-section strands or square cross-section strands. Althoughonly two strand cross-sections are discussed herein, strands havingvarious cross-sections are possible. Further, this is true with most ofthe designs for the unit cell.

To create the mesh as shown in FIG. 10, the unit cell can be instancedacross the 3-D space to produce the required lattice. FIG. 11illustrates a view of a diamond lattice structure with and without laserbeam compensation. Laser beam compensation essentially allows thediameter of the beam to be taken into account. Without it theconstructed geometry is one beam diameter too wide as the beam tracesout the contour of the particular section being grown. When laser beamcompensation is utilized, the contour is offset half a beam diameter allaround the constructed geometry which is represented in the CAD file.Although various parameters may be used, the parameters employed tocreate the lattices of FIG. 11 include a laser power of 90.5 watts withan exposure time of 1,000 μsec from a point distance of 90 μm. Table 3illustrates various other examples of parameters that may be used tocreate various unit cells.

TABLE 3 edge laser point length diameter power exposure distance Partbuild on SLM μm μm Watts μsec μm Diamond Structure 2000 200 90.5 1000 90Diamond Structure 2000 200 90.5 1000 90 with compensation Dodecahedron1500 200 68.3 1000 90 Structure Dodecahedron 1500 200 68.3 1000 90Structure with compensation Modified 1500 200 90.5 1000 90 TruncatedOctahedron

As shown in FIGS. 9B and 12, the porous structure can also be createdusing a unit cell in the shape of a dodecahedron. The regulardodecahedron is a platonic solid composed of 20 polyhydron vertices, 30polyhydron edges, and 12 pentagonal faces. This polyhydron is one of anorder of five regular polyhedra, that is, they each represent theregular division of 3-dimensional space, equilaterally andequiangularly. This basic unit cell for a decahedron mesh can be builtup in a CAD package using the following calculations and procedure. Thedodecahedron has twelve regular pentagonal faces, twenty vertices, andthirty edges. These faces meet at each vertex. The calculations for aside length of a dodecahedron are given by simple trigonometrycalculations and are known by those in the art.

In a method of use, a sweep feature is first used to model thedodecahedron structure by driving a profile along a trajectory curve.The trajectory curves are constructed from datum points corresponding tothe vertices of the dodecahedron connected by datum curves. The type ofprofile remains constant along the sweep producing the model shown inFIG. 9B. The size and shape of the profile can be designed to suit theparticular application and the required strut diameter. Once aparticular unit cell has been designed, the cell can be instanced toproduce a regular lattice as shown in FIG. 12. As a dodecahedron is notspaced filling, meshes are produced by simple offsetting of the unitcell and allowing some of the struts to overlap. This method ofoverlapping may be used with the alternate shapes of the unit cell.

FIG. 13 shows a view of a dodecahedron (with and without laser beamcompensation, from left to right) structure using selective lasermelting process parameters. Once again, although the parameters may bevaried, the lattices of FIG. 13 were created using the followingparameters; a laser power of 90.5 watts, exposure of the powder for1,000 μsec and a point distance of 90 μm.

As shown in FIGS. 9C and 14, the unit cell of the present invention mayalso be constructed in the shape of a truncated octahedron. A truncatedoctahedron has eight regular hexagonal faces, six regular square faces,twenty-four vertices, and thirty-six edges. A square and two hexagonsmeet at each vertex. When the octahedron is truncated, it creates asquare face replacing the vertex, and changes the triangular face to ahexagonal face. This solid contains six square faces and eight hexagonalfaces. The square faces replace the vertices and thus this leads to theformation of the hexagonal faces. It should be noted here that thesetruncations are not regular polydra, but rather square-based prisms. Alledges of an archamedian solid have the same length, since the featuresare regular polygons and the edges of a regular polygon have the samelength. The neighbors of a polygon must have the same edge length,therefore also the neighbors and so on. As with previous unit cells,various dimensions such as the octahedron height, octahedron volume,octahedron surface area, octahedron dihydral angle, and truncatedoctahedron volume, truncated octahedron height, truncated octahedronarea, truncated octahedron volume, truncated octahedron dihydral anglecan be determined by simple trigonometry and are known by those skilledin the art.

In a method of use, a CAD model of the truncated octahedron isconstructed using the sweep feature and calculations and dimensions areincorporated using basic trigonometry. To tessellate the unit cell, theunit cell is first reoriented to enable easy tessellation and to reducethe number of horizontal struts in the model. Further, the model can bemodified to remove all of the horizontal struts as shown in FIG. 9D. Themodified structure is reproduced in order to save file size in theSteriolithography (“STL”) format of the program. Next, in order tocreate the unit cells, the method of using a laser melting process isperformed. In one preferred embodiment, the parameter chosen includes alaser power of 90.5 watts, an exposure of 1000 μsec with a pointdistance of 90 μm. FIG. 8B illustrates a lattice structure formed usinga plurality of individual truncated octahedron. As discussed earlier,the removal of various struts can create a barb effect on the exteriorsurface of the lattice structure.

As shown in FIGS. 15A-D, it is possible to reduce the size of the unitcell geometry. Also as shown, it is possible to manufacture open cellstructures with unit cell sizes below 1 millimeter. FIG. 15A illustratestruncated octahedron structures manufactured using the laser meltingprocess. All the structures were created using a laser power of 90.5 W,and a point distance of 90 μm; however, from left to right, the exposuretime was varied from 500 μsec and 100 μsec. FIG. 15 illustrates similarstructures and parameters as used with FIG. 15A, however, the unit cellused to create the lattice is diamond. FIGS. 9C and 9D illustrate a sideview of the truncated octahedron structure of FIG. 15A and the diamondstructure of FIG. 15B, respectively. Table 4 includes variousmanufacturing parameters used to construct various unit cell structure.

TABLE 4 Length Width Strand of of Laser Point Part build length strandstrand Power Exposure distance on SLM μm c/s μm c/s μm Watts μsec μmTruncated 3000 50 50 90.5 500 90 Octahedron Truncated 3000 50 50 90.5300 90 Octahedron Truncated 3000 50 50 90.5 100 90 Octahedron Truncated1000 50 50 90.5 500 90 Octahedron Truncated 1000 50 50 90.5 300 90Octahedron Truncated 1000 50 50 90.5 100 90 Octahedron Diamond 700 50 5090.5 500 90 Structure Diamond 700 50 50 90.5 300 90 Structure Diamond700 50 50 90.5 100 90 StructurePseudorandom representative geometries may be made from the currentregular unit cells by applying a random X, Y, Z perturbation to thevertices of the unit cells. One such example can be seen in FIG. 16. Inanother aspect of the present invention, various freestanding constructscan be generated.

Various other methods may also be utilized to produce the bone ingrowthstructure 14, bearing support structure 12 and/or the intermediatestructure 16 of the acetabular cup 10 in methods known to those in theart.

In one preferred embodiment, the average pore size of the bone ingrowthstructure 14 falls within 280 μm to 480 μm, as measured usingconventional linear intercept methods. A bimodal pore size distributionmay be present as, for example, small pores within a 250 μm to 450 μmrange and larger pores within a 600 μm to 800 μm range. The metal insert11, i.e., the bone ingrowth structure 14, the bearing support structureand the intermediate structure 14 may be isotropic as, for example,without directionality with regard to the structure, and mechanicalproperties.

In one preferred embodiment, the average pore sizes of the porous layer14 for interconnecting pores exceeds 250 μm with at least 99% and thepore volume therefore within between 65% to 75% of interconnecting poresexceeding 180 μm.

The general thickness of the porous layer generally lies within therange of between 1 mm to 2 mm but may be larger or smaller if sorequired.

The porous structure 14, bearing support structure 12 and theintermediate structure 16 may be formed simultaneously using any of theprocesses described herein or a combination of the processes.

Once the metallic structure has been formed, e.g., the bone ingrowth,bearing and intermediate structures, a polymeric material may beconnected to the bearing support structure 12 to enable the acetabularcup 10 to bear against an articulating surface of an additional element.The polymeric material will comprise the bearing surface 8 of theacetabular cup 10

Depending on the material used to create the bearing surface 8, thepolymeric material can be integrated with the bearing support structure12, by compression molding, injection molding or heat forming. It mayalso be possible to cast certain types of materials from solution as,for example, polyurethane.

If the polymeric material used to form the bearing surface 8 is anultra-high molecular weight polyethylene (“UHMWPE”) material or thelike, the metallic insert, i.e., the bone ingrowth structure 14, thebearing support structure 12 and the intermediate structure 16, butspecifically the bearing support structure 12, may be joined to thebearing surface 8 by a compression molding process using a matched metaldie. The metal insert 11 is placed into a cavity part of a metal die.The polymer powder may then be added to the cavity of the metal die anddesirably is dispersed against the bearing support structure 12. Thecavity of the metal die is sealed and the metal die is then heated to arequired temperature. As the temperature of the polymer powder isincreased, the polymer powder begins to soften or melt so as to beflowable. Increased pressure onto the polymer powder may also aid in themelting process. Fusion of the polymer powder and attachment to thebearing support structure 12 is achieved when the acquired applicationof heat and pressure is reached. Subsequent cooling under pressureallows solidification of the polymer powder, which thus forms thebearing surface 8 that is securely attached to the bearing supportstructure 12. A final machining operation may be required to completethe construct of the bearing surface 8.

In one preferred embodiment, the metal insert 11 is situated in themetal die with the bone ingrowth structure 14 bounded within the cavityof the metal die such that the polymer material cannot come in contactwith the bone ingrowth structure. And since the intermediate structure16 is preferably substantially solid, the intermediate structureprohibits or at least, reduces the ability of the polymeric material tocome in contact with the bone ingrowth structure as the polymericmaterial attaches to the bearing support structure 12 to form a bearingsurface 8. By keeping the pores of the bone ingrowth structureunencumbered with polymer material, the ability of the bone ingrowthstructure to promote bone ingrowth is not altered.

In an alternate embodiment, an injection molding process may be carriedout in order to fuse the bearing surface 8 to the bearing supportstructure 12. An injection molding process may be preferred when thematerial used to create the bearing surface 8 is a polyurethane orchopped-fiber-reinforced poly (ETHERETHERKETONE) (“CFRPEEK”). Similar tothe compression molding process, in the injection molding process, themetal insert 11 is secured into a cavity of an injection molding machineand the mold closed. As with the previous embodiment, the bone ingrowthstructure 14 may be isolated from the polyurethane or additional polymerused. The selected material, e.g., polyurethane or CFRPEEK is heated ina barrel of the injection molding machine. Once the selected material isheated in the barrel of the injection mold, the pressure may be appliedto the selected material to urge the heated selected material from thebarrel into the mold cavity and onto a surface of the bearing supportstructure 12. Upon cooling, the selected material is fused to thebearing support structure 12 so as to form the bearing surface 8 uponwhich the acetabular cup 10 may move relative to an additional element,i.e., the femoral stem FS. Upon cooling, the completed part may beremoved from the injection mold and machined if so required. The moldcavity can be configured such that particular features, designs andcontours of the bearing surface 8 may be formed.

In still yet another alternate embodiment, the bearing surface 8 may beformed using a heat forming process. In a heat-forming process,materials such as UHMWPE are supplied as fabricated rod stock suitablefor machining. Profiles can be produced by machining the fabricated rodstock to represent a near net shape of the intended article such as thebearing surface 8 of the acetabular cup 10. Once the article has beenproduced, both the metal insert 11 and the shape polymer machine partare placed into a mold and heated to the required temperature. Upon theapplication of heat and pressure, the softened polymer is forced intoand against the metal insert 11, specifically the bearing supportstructure 12. Upon cooling, solidification takes place and the polymeris secured to the metal insert 11 and specifically the bearing supportstructure 12. Further machining may be required if necessary once thepart has been allowed to cool and is removed from the mold.

As with previous embodiments, in combination with the intermediatestructure 16 and additional elements, the bone ingrowth structure 14 maybe isolated from any polymeric material so that the polymeric materialcannot affect the ability of the structure to promote bone ingrowth.

In yet still another alternate embodiment, the bearing surface 8 may beconstructed using a solution casting method. In a solution castingmethod, a material, such as a polyurethane material, can be formed bycasting solvent-dissolved solutions in the mold.

In addition to the method as described above, it is also possible tomake the bearing surface 8 out of additional material such as a metallicmaterial or ceramic material. As such, when forming the bearing surface8 from a metallic material, the selective laser melting process,described herein, as well as in U.S. patent application Ser. Nos.10/704,270, and 11/027,421 (described above) may be utilized.

An example of a process for forming the acetabular cup 10 is discussedherein, although various methods may be employed. In a preferred method,software and equipment, as shown in Table 6 below, may be employed tobuild a finished product.

TABLE 6 Equipment/Software Description MCP realiser SLM machine using100 w fibre laser Magics V8.05 (Materialise) CAD software package usedfor manipulating STL files and preparing builds for Rapid Manufacture(RM) Manipulator 3.4.1 Propriety program for populating a solid STL filewith porous surface coating. Outputs a sliced F&S file ready formanufacture Fusco MCP realiser operating software Gas atomized co -titanium Metal powder with a mean powder particle size of approximately40 μm

In a first step of such process, a CAD file of an acetabular cupcomponent is loaded into the Magics software package as a single part,as shown in FIG. 17. The file may then be divided into three separatesolid volumes having a 1.1 mm thick outer layer—this layer will be usedto create the 80% porous bone ingrowth surface; 0.1 mm thickintermediate layer—this layer will be a fully dense layer that supportsthe bone ingrowth surface; and 0.8 mm thick inner layer—this will beused to create an interlock surface for a polymer injection molding. Thethree layers, when completed, will comprise the metal insert 11 of theacetabular cup 10.

A completed acetabular cup 10 is shown is shown in FIG. 17 and includesa bearing surface 8, an intermediate structure 16 and a bone ingrowthstructure 12. The bone ingrowth structure 14 may include fins orprotrusions 13 for anchoring into bone.

In an alternate embodiment of the present invention, the acetabular cupmay be constructed with a two tier structure. As shown in FIG. 18, whichis a cross section of an acetabular cup 110, the two tier structureincludes a metal insert 111 having a bone ingrowth structure 114 and abearing support structure 112. The bearing surface 108 is attached tothe bearing support structure 112 are connected directly to one another.But each structure is adapted for its own purpose, i.e., the boneingrowth structure 14 has a porosity adapted for bone ingrowth and thebearing support structure 12 has a porosity suited for anchoring apolymeric material or additional material as discussed herein.

Although, the figure illustrates a demarcation between the twostructures, highlighting the difference in porosity between the two, theactual metal insert 111 may have a graded porosity which increases,decreases or some combination of the two along an axis 119 passingthrough the center of the acetabular cup 110.

In yet another alternate embodiment, as shown in FIG. 19, the acetabularcup 210 may have a plurality of structures comprising a metal insert211. The metal insert 211 may include a bone ingrowth structure 214, anintermediate structure 216 and a bearing support structure 212. Theintermediate structure 216 may include a first barrier 217, a secondbarrier 218 and a bridging structure 219. The first barrier 217 andsecond barrier 218 may be substantially solid while the bridgingstructure 219, positioned between the two barriers has a particularporosity. The particular porosity may be specifically designed totransfer mechanical loads through the overall construct to a bone towhich the acetabular cup is attached to. Once the metal insert 211 isdesigned, the bearing surface 208 may be coupled thereto as describedherein.

Although the present invention has been discussed with regard toconstructing an acetabular cup, various other orthopedic implants,tools, apparatus, and structures may also be built using the sameprocess. For instance, a patella component 300, as shown in FIGS. 20 and21, includes a baseplate 302 and a bearing surface 304.

As with the acetabular cup discussed herein, once the baseplate 302 hadbeen constructed, the patella bearing surface 304 may be attached to thebaseplate 302 using the processes discussed herein.

In a method of assembly, the patella is shaved on a posterior side to adesired depth and some of the cartilage surrounding the area is removed.The baseplate 302 of the patella component preferably includes aplurality of pegs 306 that engage the remaining bone of the patella. Thepegs 306 are designed for bone ingrowth as discussed in here. With thepegs 306 attached to the posterior of the patella, the bearing surface304 may replace and perform the function of any cartilage removed fromthe area.

In yet another alternate embodiment, as shown in FIGS. 22 and 23, thepresent invention can be used to construct a cartilage plug 400. Thecartilage plug 400 desirably includes a metal insert 401 having a boneingrowth structure 402, an intermediate structure 403 and a bearingsupport structure 404. The metal insert 401 may be constructed usingmethods discussed herein. Once the metal insert 401 is completed, thebearing surface 408 may be attached to the bearing support structure 404as discussed herein.

For illustration purposes, the bearing support structure 404 iscomprised of two independent lattices 406 and 407. The lattices 406 and407 are independent from one another and may be constructed differentlyfrom each other. In alternate embodiments, the bearing support structure404 may be constructed similar to the bearing support structure 12 ofthe metal insert 11, discussed herein.

The cartilage plug 400 may be employed as for example when only aportion of a tibial plateau must be replaced. A bore is created in thetibial plateau removing the defective portion and than filled with thecartilage plug 400. The bone ingrowth structure 514 of the cartilageplug 400 is positioned within the bone while the bearing surface 408faces outward to replace any cartilage removed from the area.

In yet another alternate embodiment not shown in the figures, theintermediate structure of an implant may be constructed using a die castor any method known to those in the art. The resultant intermediatestructure may then be placed onto the base plate of an apparatus similarto that shown in FIG. 4 or 5. Once in place, a bone ingrowth structureand bearing support structure may be built onto the intermediatestructure.

As previously discussed, a bearing surface may be attached to an implantor metal insert indirectly. For example, as shown in FIG. 24, a metalinsert 511 may be constructed similar to metal insert 11 in the shape ofan acetabular cup 510, and include a bone ingrowth structure 514, anintermediate structure 516 and a bearing support structure 512. A bonecement 506 may be deposited and attached to the bearing supportstructure 512, in methods known to those in the art. A UHMWPE liner 509is positioned adjacent the bone cement and is subsequently attachedthereto as the bone cement polymerizes. The liner 509 preferablyincludes an exterior 502 and an interior 503. The exterior 502 of theliner 509 preferably includes a plurality of attachment sites such asradial grooves or as shown in the figure, circumferential grooves 504.As the liner 509 is forced against the bone cement the bone cementengages the grooves. As the bone cement 506 polymerizes, the liner 509is mechanically interlocked to the bone cement.

The interior 503 of the liner 509 is suitable to act as a bearingsurface of the completed acetabular cup 510. Preferably, the metalinsert 511 and liner 509 are prepackaged and available to a surgeon in aplurality of sizes such that during surgery the surgeon only has toremove the desired liner and insert once the specific measurements andrequirements have been decided upon.

Systems incorporating the used of a liner cemented to a porous metalinsert are normally used when the acetabullum has been severely damagedor in some cases of revision surgery.

Although not shown in the figures, the present invention may be in theshape of a glenoid or any other component where bone ingrowth is desiredin combination with a bearing surface.

As with all of the embodiments herein, it is possible to apply a coatingof a bone growth enhancer as, for example, hydroxyapatite,bonemorphogenic protein such as OP-1 (Stryker), to the surface intendedto be in direct contact with bone.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. A medical implant comprising: a metal insert having a bone ingrowthstructure, an intermediate structure and a bearing support structure,said bone ingrowth structure having a porosity sufficient to promotebone ingrowth; a bearing surface formed from a polymer material, saidbearing surface being attached to said bearing support structure;wherein said intermediate structure has a porosity sufficient to inhibitsaid polymer material from translating through said bearing supportstructure to said bone ingrowth structure.
 2. The medical implantaccording to claim 1, wherein said intermediate structure is designed tofacilitate a specific stiffness characteristic to an overall construct.3. The medical implant according to claim 1, wherein said intermediatestructure includes two barrier layers and a bridging section.
 4. Themedical implant according to claim 2, wherein a bone cement is depositedonto said bearing support structure.
 5. The medical implant according toclaim 4, wherein said bearing surface is part of a liner, said linerhaving an exterior and an interior, said interior adapted to act as abearing surface, said exterior adapted to engage said bone cement. 6.The medical implant according to claim 1, wherein said metal insert isin a shape of an actebular cup.
 7. The medical implant according toclaim 1, wherein said metal insert is in the shape of a cartilage plug.8. The medical implant according to claim 1, wherein said metal insertis in the shape of a patella component.
 9. The medical implant accordingto claim 1, wherein said bearing support structure includes at least onelattice.
 10. The medical implant according to claim 1, wherein said boneingrowth structure has a graded porosity.
 11. The medical implantaccording to claim 1, wherein said bone ingrowth structure includes afirst portion having a first porosity and a second portion having asecond porosity, said first porosity being different than said secondporosity.
 12. The medical implant according to claim 1, wherein saidbone ingrowth structure has a thickness of between 1 mm and 2 mm, saidintermediate structure has a thickness of less than approximately 0.25mm, said bearing structure has a thickness greater than approximately0.5 mm.
 13. The medical implant according to claim 1, wherein said boneingrowth structure has a thickness of less than 1.5 mm, saidintermediate structure has a thickness of less than approximately 5 mm,said bearing structure has a thickness greater than approximately 0.5mm.
 14. The medical implant according to claim 1, wherein said metalinsert and said bearing surface have a thickness of less than 4 mm. 15.The medical implant according to claim 1, wherein said bone ingrowthstructure has a pore size distribution in the range of 80 μm to 800 μm,said bearing support structure has a pore size distribution higher than800 μm.
 16. An implant comprising: an intermediate structure havingfirst and second sides; a bone ingrowth structure formed on the firstside; a bearing support structure formed on the second side; and abearing surface attached to the bearing support structure, wherein theintermediate structure inhibits any portion of the bearing surface fromtranslating through the bearing support structure to the bone ingrowthstructure.
 17. The implant of claim 1, wherein the intermediatestructure, bone ingrowth structure, and bearing support are formed ofmetal and the bearing surface is formed of polymer.
 18. The implant ofclaim 17, wherein the implant is an acetabular cup replacement implant.19. The implant of claim 17, wherein the implant is a patellareplacement implant.
 20. An implant comprising: an intermediatestructure having first and second sides, two barrier layers and abridging section, the intermediate structure having a thickness lessthan 5 mm; a bone ingrowth structure formed on the first side, the boneingrowth structure having a thickness of between 1 mm and 2 mm; abearing support structure formed on the second side, the bearing supportstructure having a thickness greater than 0.5 mm; and a bearing surfaceattached to the bearing support structure, wherein the intermediatestructure inhibits any portion of the bearing surface from translatingthrough the bearing support structure to the bone ingrowth structure.